Production of organic acid esters of cellulose



, the. fcellulosic material.

Patented July 15, 1952 2,603,638 e y I memories OF ORGANIC ACID EST-ERS or CELLUL'OSE? George W. Seymour, Maplewo'od, Pdaiuiihe B. White, Summit, andMark .Plunguian, Gillette,

assignors to Celan'ese Corporation of America, New York, N;-'Y., a corporation 'o'f Delaware .No Drawing. Application December 22, 1950,

Serial N0. 202,406

v g 1 This invention relates to the production of organic acid esters of cellulose and relates more particularly to an improved process for the production of organic acid esters of cellulose which may be carried out in a. continuous manner.

This application is a continuation-in-part of application S. No, 115,946, .filed September 15, 1949. v

In the production of organic acid esters of cellulose by the esterification of a cellulosic material, it i's customary' to pretreat the cellulosic material before 'esteri'fication to increase its reactivity and thereby reduce the total esterification time. To enabl'e'ithe production of the organic acid esters of cellulose to be carried out in'a continuous manner, the pretreatment should require only a relativ'ely'short period of time. In addition, the pretreatment should increase the reactivity of the cellulosi'c material-to a point where the esteri- *fication thereof will be completed rapidly.

It is an important object of this invention to provide a process for the productionof organic acid esters of cellulose which Will-fulfill the foregoing requirements and which may be carried out in a continuous manner.

"a novel process for 'pretreating cellulosic mate- "rial which may be 'carried' out in'a relatively short period of time and which-will render said cellulosic material highly reactive.

Other objects of this invention will be apparent from the I following detailed description and claims.

In accordance with the present invention, cellulosic material is subjected to a' twostage pretreatment priorto esterii'lcation. During the first stage of the pretreatment, thecellulosiomaterial has-"added thereto-a lower aliphatic acid in the presence of "from about i 'to9 parts by weight of water, 'or preferably from about '4; to '7 parts by weight of water for each 100 parts by weight of I After all the treating agents have been added to'the cellulosic material for thefirst stage'of thejpretreatment,an interval of at least about 2 minutes, or preferably at least about '3 minutes, is permitted to elapse. Then, the cellulosic' material hasadded thereto, during the second stage of the pretreatment, which does notexceed aboutlli minuteaanadditional quantity or a lower aliphatic acid containing from about? to 15 parts by weight of an'esterification catalyst icr'eaeh 100 parts by'weight pi the cellulosic'material. j 7 f J The pieces of 'Ltfh'e presentfinvention "may be 'appliedto" any suitable cellulos'i'c material; such 7 Claims, (or. "zet -'22s) .the first stage of the pretreatment in amounts of from. about 15 to 'l5parts byweightor preferably from about 'tof l'oparts'by weight for each 100 1 pretreatmenafrom about 4 to 9 parts'by weight as cotton .l'inters', or wood pulps or the like from which the lignin, pentosan, resins and similar constituents have been removed, as, for example, purifiedv sul-fite pulp, sulfate pulp or soda pulp. In addition, there may be employedcellulosic material derived from other sources such as bamboo, reeds, jute, 'esparto, straws such as linseed and lhempseed straw, grasses, peanut hulls,

bark, etc. The cellulos'ic material may be pretreatedin the 'form ofa massof loose fibers, or in the form .ofv a sheet, strip or board. The term cellulosic material as employed herein is to be construed as meaning cellulose which may contain smaller quantities of othersubstances such as the residual impurities that remain therein following the purification processes referred to above. l

.Any of the lower aliphatic acids including formic, acetic,-propionic and butyric acids, as well as mixtures thereof, may be employed during parts by weight of the" c'ellulosic material. There must also be presen-tduring the first stage of the of waterl,'for each. 100 a parts by weight of the cellulosic' material. The necessary amount of Watermaybe present in or may be added to the cellulosic material before the pretreatment begins, or it may be included in the lower aliphatic acid employed for the pretreatment, or a portion ofthewater may be .presen't in or added to the 'e'e1lulosic fmaterial before the pretreatment begins and the remainder of the water may be me 7 eluded in the lower aliphatic acid.

The temperature employed during the first stage of the pretreatment is not critical and may range from about 25 to 55C. To obtain a cellulosic material having the 'hig'hest'r'eactivity, a short interval of time should be permitted to elapse after all the treating agents have been added to the cellulosic materials for the first stage of thepretreatment and before the second stage of the pretreatment is begun; At temperatures of up to about 3'5;C.;-thisinterval should-be at fleas'it' about 3"mir' 'ute'sQ At higher temperatures, an interval of at least about 2 minutes "will be adequate. 1 in the second stage of the pretreatment, by the treatment of the cellulosic material, for a period "notfe'xcee'ding about 15" minutes and; preferably between' 'about 2"and-f5'-minutj i tional quantity of a lower aliphatic --aeia-,eqmaiii The first stageof the pretreatment is" renewed,

with an addii 41f. the teena e; m ss-inter. I

ing from about 3 to parts by weight of an 100 parts by weight of the cellulosic material. Any of the known acid cellulose esterification catalysts may be employed for pretreating the,

cellulosic material in accordance with the process of this invention, but it is preferred to employ sulfuric acid for'this purposesince it produces a cellulosic material havingv the"highest reac 15 tivity in the shortest period of time.

The pretreating agents may be applied to the cellulosic material in any desired manner. For example, they may be sprayed or rolled ontothe cellulosic material, or, when the cellulosic material is in the form of a sheet, strip or board, the pretreatingagents may be applied as a continuous film from a perforated or slotted conduit extending the width of the sheet, strip or board.

The pretreatedcellulosic material is esterified with an organic acid anhydride, which may contain additional quantities of lower aliphatic acid and esterification catalyst. Esterification proceeds rapidly and is completed in about 15 to 30 minutes, or less. The lower aliphatic acid acts as a solvent for the cellulose ester so that the product is obtained in the form of a clear dope. 7

After the esterification is complete, a sufiicient quantity of water is addedto theesterification mixture to convert any remaining organic acid anhydride to the corresponding acid, following which the cellulose ester, preferably after the addition of a further quantity of water, is permitted to hydrolyze or ripen to impart the desired solubility characteristics thereto. The cellulose ester is then precipitated from the esterification mixpurities, stabilized'if necessary,'washed again and finally dried. When the process of this invention is erhployedfor the preparationof organic acid esters of cellulose,1it is possible to carry out both 1 thepretreatment and esterification on a continuture, washed to free it from acids andother imous rather'than on a batch basis, since the time v .required for both steps is sufficiently short to render a continuous process feasible. I

' Our invention will now be describedspecifically 'in connection withthe production of cellulose acetate, which is commercially the most important organic acid ester of cellulose at the present time. It may, however, also be employed'for the production of otherv organic acid esters of cellulose such as, for example, cellulose propionate, cellulose butyrate," cellulose acetate propionate and cellulose acetate butyrate.

The following examples are given to illustrate this invention further.

' iETrampl eI Onto 100 parts by weight of cotton linters containing 6 parts by weight of water, there is sprayed Q35 partsaby weight of acetic acidand the cotton linters are stirred for 5 minutes. The cotton Qlinters are then sprayed with 300 parts by Weight of acetic acid containing 15 parts by weight of sulfuric acid. Afteran interval of lminutes, the

. pretreated cotton linters are esterified by treatfmientwith 220 parts by weight of acetic anhydride at a temp erature of 35fflC.- Esterificationis com- ;pletein 15 ;minute s as V evidenced by the clearing Example II Cotton linters are pretreated and esterified in .the manner set forth in Example I, employing 10 parts by weight of sulfuric acid during the second stage of the pretreatment and adding 5 parts by weight of sulfuric acid'to the acetic anhydride employed for the esterification of the pretreated cellulosic material. Esterification is complete in 15 minutes as evidenced by the clearing of the esterification mixture.

Example III Cotton lintersfare pretreated and esterifled in the manner set forth in Example I, employing 3 parts by weight of sulfuric acid during the second stage of the pretreatment and adding 12 parts by weight of sulfuric acid to the acetic anhydride employed for the esterification of the pretreated cellulosic material. Esterification is complete in 16 minutes as evidenced by the clearing of the esterification mixture. 7

Whenthe quantity of sulfuric acid employed during the second stage of the pretreatment is reduced below about 3 parts by weight per parts by weight of cellulosic material, the time required for esterification increases rapidly and, in

many cases, the esterification does not go to completion.

' Example IV Onto 100 parts by weight of cotton linters that have been dried for 2 hours at'100 C. and contain 0,.3'parts by weight of water, there is sprayed 351parts byweight of acetic acid'containing 6 parts by weight of water and the cotton linters are permitted to stand for 3 minutes. The cotton linters are hen sprayed with 300 parts by weight of acetic acid containing 15 parts by weight of sulfuric acid. After an intervalof 1 minute, the pretreated cotton linters are esterified by; treatment with 220 parts by weight of acetic anhydride'at a temperature of-35" C. Es-

terification isjcomplete in 15 minutes.

If the water is omitted from the acetic acid employed during the first, stage of the, pretreatment, the esterification does not go to completion. It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be made therein without departing from the spirit of our inventionf V Having described our invention, what we desire to secure by Letters Patent is:

1. In a process for thepreparation of organic acid esters of cellulose from cellulosic material, the steps which comprisesubjecting the cellulosic material to a multi-stagepretreatment prior to esterificatiomone stageof said pretreatment comprising the additionto the cellulosic material of a lower aliphatic acid in the presence of from about-4' to 9 parts by weight of water for each100 parts by weight of the cellulosic material, and

another stage of said pretreatment comprising -the addition to the cellulosic material of a lower aliphatic acid containing from about 3 to 15 parts by weight of an esterification catalyst riod' of less than about 15 minutes after the.addi-,

,tion thereto of the lower aliphatic acid esterification catalyst. 2. Process. according to claim 1, wherein from and the acid for each 100 parts by weight of cellulosic material are employed during the initial stage of the pretreatment, and from about 100 to 600 parts by weight of lower aliphatic acid for each 100 parts by weight of cellulosic material are employed during the second stage of the pretreatment.

3. Process according to claim 2, wherein there is an interval of at least about 2 minutes between the two stages of the pretreatment, and wherein acetic acid is employed as the pretreating acid and sulfuric acid is employed as the esterification catalyst;

4. In a process for the preparation of cellulose acetate from cellulosic material, the steps which comprise subjecting the cellulosic material to a multi-stage pretreatment prior to esterification, one stage of said pretreatment comprising the addition to the cellulosic material of a lower aliphatic acid in the presence of from about 4 to 9 parts by weight of water for each 100 parts by weight of the cellulosic material, and another stage of said pretreatment comprising the addition to the cellulosic material of a lower aliphatic acid containing from about 3 to 15 parts by weight of an esterification catalyst for each 100 parts by weight of cellulosic material without displacing any of the lower aliphatic acid contained in the cellulosic material, and acetylating the pretreated cellulosic material within a period of less thanabout 15 minutes after the addition thereto of the lower aliphatic acid and the esterification catalyst.

5. Process according to claim 4, wherein from about 15 to,75 parts by weight of lower aliphatic acid for each 100 parts by weight of cellulosic material areemployed during the initial stage of the pretreatment, and from about 100 to'600 parts by weight of lower aliphatic acid for each 100 parts by weight of cellulosic material are employed during the second stage of the pretreatment. 1 V

6. Process according to claim wherein there is an interval of at least about 2 minutes between the two stages of the pretreatment, and wherein acetic acid is employed as the pretreating acid presence of from about 4 to 7 parts by weight of water for each parts by weight of cellulosic material, and another stage of said pretreatment comprising the addition to the cellulosic material after an interval of at least about 3 minutes of from about to 300 parts by weight of acetic acid and from about 3 to 15 parts by weight of sulfuric acid for each 100 parts by weight 01' .cellulosic material without displacing any of the acetic acid contained in the cellulosic material, and acetylating the pretreated cellulosic material within a period of less than about 15 minutes after the addition thereto of the acetic acid and sulfuric acid.

GEORGE W. SEYMOUR. BLANCHE 13. WHITE. MARK PLUNGUIAN.

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7. IN A PROCESS FOR THE PREPARATION OF CELLULOSE ACETATE FROM CELLULOSIC MATERIAL, THE STEPS WHICH COMPRISE SUBJECTING THE CELLULOSIC MATERIAL TO A MULTI-STAGE PRETREATMENT PRIOR TO ESTERIFICATION, ONE STAGE OF SAID PRETREATMENT COMPRISING THE ADDITION TO THE CELLULOSIC MATERIAL OF FROM ABOUT 30 TO 40 PARTS BY WEIGHT OF ACETIC ACID FOR EACH 100 PARTS BY WEIGHT OF ACETIC ACID FOR EACH PRESENCE OF FROM ABOUT 4 TO 7 PARTS BY WEIGHT OF WATER FOR EACH 100 PARTS BY WEIGHT OF CELLULOSIC MATERIAL, AND ANOTHER STAGE OF SAID PRETREATMENT COMPRISING THE ADDITION TO THE CELLULOSIC MATERIAL AFTER AN INTERVAL OF AT LEAST ABOUT 3 MINUTES OF FROM ABOUT 150 TO 300 PARTS BY WEIGHT OF ACETIC ACID AND FROM ABOUT 3 TO 15 PARTS BY WEIGHT OF SULFURIC ACID FOR EACH 100 PARTS BY WEIGHT OF CELLULOSIC MATERIAL WITHOUT DISPLACING ANY OF THE ACETIC ACID CONTAINED IN THE CELLULOSIC MATERIAL, AND ACETYLATING THE PRETREATED CELLULOSIC MATERIAL WITHIN A PERIOD OF LESS THAN ABOUT 15 MINUTES AFTER THE ADDITION THERETO OF THE ACETIC ACID AND SULFURIC ACID. 